A conventional laser printer has a main casing, and, within the main casing, a process unit retaining a photosensitive drum and a developing roller is detachably mounted. A toner box in which toner is accommodated is mounted in the process unit.
The photosensitive drum and the developing roller are disposed in the process unit such that a circumferential surface of the photosensitive drum is in contact with a circumferential surface of the developing roller. The process unit has a curved wall at a position opposite the photosensitive drum relative to the developing roller. The curved wall is formed so as to conform to an outline of the toner box. The process unit is further provided with a toner box accommodating chamber for accommodating the toner box at a position opposite the photosensitive drum and the developing roller relative to the curved wall. The toner box accommodating chamber includes a shutter movable along the curved wall. The curved wall is formed with a toner inlet port penetrating the curved wall. The curved wall has a surface confronting the shutter, and a seal member is affixed to the surface to encircle the toner inlet port. That is, the seal member is formed with a seal opening aligned with the toner inlet port.
The toner box is mounted in the toner box accommodating chamber in alignment with the photosensitive drum and the developing roller. After the toner box has been mounted in the toner box accommodating chamber, the toner box is pressed toward the curved wall in the alignment direction, that is, a direction the same as a mounting direction of the toner box with respect to the toner box accommodating chamber. Then, the shutter is moved to a position displaced from the toner inlet opening.
As a result, the shutter is displaced from a position between the seal member and the toner box, and the seal member and the toner box are brought into pressure contact with each other. Consequently, the periphery of the toner inlet port is sealed between the curved wall and the toner box by the seal member. In this state, the interior of the toner box and a space in which the photosensitive drum and the developing roller are accommodated have a fluid communication with each other through the toner inlet port, allowing toner to fluidly circulate between the space and the interior of the toner box.